This invention relates to an improved vacuum augmentation device for a vehicular brake device.
There has been proposed and practically employed a vacuum augmentation device of the type which has a diaphragm dividing an outer shell into two chambers and receiving a differential pressure on the opposite sides thereof which is transferred through a piston plate on one face of a plurality of reaction levers to an output rod to produce a reaction force which is transferred to the other face of the reaction levers and then to an input rod.
In the vacuum augmentation device of the type referred to hereinabove, in order to provide the fulcrums for the reaction levers, a metal mounting plate member interposed between the reaction levers and the piston plate has pins formed of hard wire retained thereon.
In the prior art vacuum augmentation device referred to hereinabove, one pin is associated with each of the reaction levers, and usually the number of pins employed is the same as the number of reaction levers; means for retaining the pins on the mounting metal plate member are provided by pawls formed by pressing and bending the mounting metal plate member at selected areas; and the fulcrum pins are retained between the pawls to position and hold the fulcrum pins for the reaction levers in position.
In the prior art vacuum augmentation device, taking possible error in the processing of parts and easiness of the assembly of parts into consideration, it is necessary to provide some radial clearance between the pin and the pin retention pawls. However, such clearance can not always assure firm retention of the pins and the pins may come off the mounting plate member in the assembly and/or use of the device. And since the pin can move within the clearance, the prior art vacuum augmentation device has the disadvantages that the vacuum augmentation ratio fluctuates from its original setting and that hysteresis increases. Furthermore, after prolonged use of the device, the mounting plate member is subjected to wear as the result of the displacement of the pins within the clearances.